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- Thermo-mechanical stresses distribution on bone drilling: Numerical and experimental proceduresPublication . Fernandes, Maria G; Fonseca, Elza M M; Jorge, Renato NIn bone drilling, the temperature and the level of stresses at the bone tissue are function of the drilling parameters. If certain thresholds are exceeded, irreversible damages may occur on the bone tissue. One of the main challenges in the drilling process is to control the associated parameters and even more important, to avoid the surrounding tissue damage. In this study, a dynamic numerical model is developed to determine the thermo-mechanical stresses generated during the bone drilling, using the finite element method. The numerical model incorporates the geometric and dynamic characteristics involved in the drilling processes, as well the developed temperature inside the material. The numerical analysis has been validated by experimental tests using polyurethane foam materials with similar mechanical properties to the human bone. Results suggest that a drill bit with lower drill speed and higher feed rate can reduce the strains and stresses in bone during the drilling process. The proposed numerical model reflected adequately the experimental results and could be useful in determination of optimal drilling conditions that minimise the bone injuries.
- The Fire Resistance of (W-W-W) Wood-To-Wood Connections Protected with Different Types of Gypsum PlasterboardPublication . Leite, Pedro; Silva, Lino; Fonseca, Elza M MThe main objective of this work is to verify the fire resistance of unprotected (W-W-W) wood-towood connections and compare the results with protected connections using gypsum plasterboard. According Eurocode 5, part 1-2 the connections could be protected by the addition of wood panelling, wood-based panels or gypsum plasterboard type A, H or F. To obtain conclusions according the application of different type of gypsum plasterboard in the designed W-W-W connections in different densities material, numerical models were building to verify the level of protection in fire action. The wood behaviour varies with temperature and its influences the progressively properties degradation. After fire exposure, it is need to determine if the charred wood connections will rest safe for use. Design methods require the use of analytical methodologies and computational modelling to predict the fire exposure and the components capacity to resist to this action. Results of the temperature field in the studied connections under fire will be presented, with the measured char layer in unprotected members and comparing the protected efficiency with different types of gypsum plasterboard.
- Fire design of wood connections loaded in shearPublication . Fonseca, Elza M M; Leite, Pedro A. S.The main objective of this work is to compare the fire resistance between wood-steel-wood (W-S-W) and wood-wood-wood (W-W-W) connections, both joined by steel dowel fasteners, in double shear. The analytical and design procedures follow simplified equations presented in Eurocode 5, part 1-1 and 1-2. A computational methodology, based on finite element method, was also implemented to produce two dimensional thermal simulations, which permits to verify the heating effect through the dowels fasteners or steel elements through the connection in study. Different cross-sections will be identified, considered as the most relevant parts, to compare the temperature distribution in the studied connections. According to the fire exposure, a thermal and transient effect will happen and a char-layer appearing in the exposure side of the connections. The measured quantity of the charred area permits to identify the lost structural material in the studied cross-sections. The charring rate will calculate and compared with the constant value proposed by the Eurocode 5, part 1-2. There are typical values for the charring rate of wood between 0.5-1.0mm/min according to Eurocode 5, part 1-2. However, as a general conclusion and additional information to help designers and professionals, the number of fasteners increases with the applied load, lower dowels diameters have higher effect in the number of fasteners, at fire exposure the steel fasteners bring the heat to inside the connections, and different wood densities affect the thermal behaviour and the charring rate evolution. The charring rate permits to quantify the lost layer thickness and the fire resistance of the connection, dependent on the chosen material density.
- Resistência ao fogo de ligações madeira-aço (W-S-W), metodologias de cálculo analítica e computacionalPublication . Miranda, Fernando; Fonseca, Elza M M; Góes, Jorge L NEste trabalho tem como objetivo apresentar metodologias de cálculo analítico e computacional, adequadas ao projeto de ligações madeira-aço (W-S-W) com chapa metálica central e ligadores do tipo cavilha em corte duplo e expostas ao fogo. Serão utilizadas as equações de cálculo simplificadas, pelo método de redução de carga, Eurocódigo 5 parte 1-1 e 1-2, na verificação da resistência ao fogo de ligações. Os cálculos de resistência ao fogo serão efetuados para o tempo de exposição 30 minutos, conforme o Eurocódigo 5 parte 1-2, tempo este capaz de ser atingido em ligações sem proteção. As mesmas ligações serão redimensionadas pelo aumento da espessura na madeira para garantia de maior resistência ao fogo. Em adição, serão desenvolvidos modelos numéricos, utilizando o método dos elementos finitos, para obter resultados da análise térmica na conjunção dos materiais da ligação.
- Wood Connections Under Fire Conditions Protected with Gypsum Plasterboard Types A and FPublication . Fonseca, Elza M M; Leite, Pedro A. S.; Silva, LinoThe wood behavior varies with temperature, which has a negative effect, be-ing verified by progressive properties degradation. After fire exposure, it is possible to measure the wood char layer and the remaining resistant cross-section area. Based on numerical models and analytical equations, it is pos-sible to study the protection level of wood connections, during fire exposure, and evaluate wood and steel dowels temperature fields in conjunction. The main objective of this work is to verify the fire resistance of unprotected (W-W-W) wood connections and compare the results with protected connections using gypsum plasterboard. According Eurocode 5, part 1-2 the connections could be protected by the addition of wood paneling, wood-based panels or gypsum plasterboard type A, H or F. To obtain conclusions according the application of different type of gypsum plasterboard in the designed W-W-W connections in different densities material, numerical models were building to verify the level of protection in fire action. Design methods require the use of analytical methodologies and computational modelling to predict the fire exposure and the components capacity to resist to this action. Results of the temperature field in the studied connections under fire will be presented, with the measured char layer in unprotected members and comparing the protected efficiency with different types of gypsum plasterboard.
- Advanced Calculation Model Calibrated with Experimental Test of Wooden Slabs Exposed to FirePublication . Fonseca, Elza M M; Piloto, Paulo A GThe wooden slabs are structural elements with wide application, in particular, in building rehabilitation, interior spaces and in new building structures. The mechanical, thermal and acoustic properties make this material as an ideal solution for floor and roof slabs applications. However, when exposed to an accidental fire condition it is necessary to assess their vulnerable behaviour accurately. In this work, an advanced calculation model is presented, based on the use of finite elements, calibrated with experimental results. The experimental tests were performed on wooden slabs exposed to a fire from below the element. The slabs were instrumented with thermocouples to measure the temperature at different control points along the fire duration in a fire resistance furnace, following the standard fire curve ISO 834. The advanced calculation model also allows the obtained the transient effect and incorporates the non-linear wood properties. The physical behaviour of the wooden slab is conditioned by the char layer formation, and this phenomenon is also considered in the advanced calculation model.
- Fire safety of wood-steel connectionsPublication . Fonseca, Elza M M; Silva, Lino; Leite, Pedro A. S.The main objective of this work is to present different analytical and computational methods which permit the safe design calculation of the wood-steel connections, under fire conditions. Wood is an anisotropic, heterogeneous and porous material and its behaviour varies with temperature. The increase of temperature influences the progressive degradation of wood properties. During fire exposure, it is need to determine if the charred wood connections are safe in use. Design methods require the use of analytical methodologies and computational modelling to predict the fire exposure and the components capacity to resist to this action. In this work, the authors present studied cases, that will help professionals to analyse wood-steel connections and focus the type of information needed to decide whether the charred elements are adequate or not to use. For the same wood-steel connections, different insulation materials will be analysed to compare their behaviour and determine the fire resistance in time domain.
- Determination of optimal parameters in drilling composite materials to minimize the machining temperature using the Taguchi methodPublication . Lopes, A.C.; Fernandes, M.G.A.; Ribeiro, J.E.P.C.; Fonseca, Elza M MThis work aims to determine the best combination of drilling parameters which results in the smaller temperature during the bone drilling procedure. An experimental procedure was adopted with the acquisition of two biomechanical blocks from Sawbones (composite material) with similar properties to the human bone. The goal of this experiment resulted in a drilling process to assess the generated temperature on the drill bit and simultaneously on the bone material. The Taguchi method is a powerful tool in high quality system design, and proved that can be used as optimization method to determine the best parameters combination to obtain the minimum temperatures in the drilling process.
- Numerical model to predict the effect of wood density in wood–steel–wood connections with and without passive protection under firePublication . Fonseca, Elza M M; Silva, Lino; Leite, Pedro ASThe main objective of this work is to present a numerical model to predict the effect of wood density in unprotected wood connections with an internal steel plate (wood–steel–wood), when comparing with the same connections using passive protection with gypsum plasterboard, submitted to fire conditions. Wood–steel–wood connections are made of four wood members, two on each side, with an internal steel plate that connects the pieces using steel dowel fasteners. First, analytical methodologies according to Eurocode 5 part 1-1 were used to design the connections at room temperature. After that, to predict the fire exposure and the connection ability, a numerical model was performed which permits to compare the fire resistance in wood–steel– wood connections without and with passive protection following the Eurocode 5 part 1-2. Results of the temperature and the wood char layer depth were compared using three different wood densities. The evolution of the charring rate was calculated in different locations of the connections and compared with the analytical value proposed by the Eurocode 5 part 1-2.
- Computational model to predict the temperature distribution produced by bone cementPublication . Oliveira, Vânia C.C.; Fonseca, Elza M MBone is the third frequent location for haematogenous dissemination of malignant tumors. Patients with multiple bone metastases are exponentially growing. Bone metastases, which are frequently diagnosed late, are associated to imminent and pathological bone fractures. Metastatic disease translates an advanced tumor stage and it has a high impact in patients’ quality of life and survival. The main objective is to study the thermal effect induced by the bone cement polymerization, in the bone metastatic tumor reduction and to understand the role of such procedure and its biomechanical stabilization. To assess the clinical effect, it is important to test this methodology before its application and obtain sustained results. In this work, a computational model was developed to predict the temperature distribution produced by cement polymerization, and verify the reduction of the metastatic tumor area due the thermal effect. Different simulations produced to evaluate the necrosis effect for two cement amount sizes introduced in a cortical and spongy bone tumor. The same computational models were reproduced introducing an endomedular nail in titanium and a femoral stem in cobalt-chrome material in pathological bone fractures.